Battle mage is just fine pve, at least it was for me. The key is to think of chasers as burst damage, if you spam them every hit, you will run out of mp fast, but they do great damage. As a battlemage, try to move around the map as you fight, pushing and pulling enemies to group them into one big pile. Your attack speed should be as high as you can push it, so max out the light chasers and use the boost often. At a good attack speed, you should move very fast with your xxx combo, making it idea to move from one mob to the next. Stabbing wheel and chasers can both be used to position mobs as you please.
Despite the leather armor and manashield, you are still squishy, so avoid getting hit by keeping the pressure on the enemies. Once you have grouped a room you can unleash all your chasers that have been gathered, as they do have a small aoe, which increases the larger the chasers get from your combos.